A photograph believed to be the only surviving image of Billy the Kid has been bought by a private collector for $2.3m (£1.4m) at auction.

Detail of the only authenticated photograph of Billy the Kid, which has been sold at an auction in Denver. Photograph: AFP/Getty Images

The black and white tintype of the 19th-century wild west outlaw was sold at auction in Denver, Colorado, and is believed to have been taken in 1879 or 1880 in Fort Sumner, New Mexico.

The hammer price, which included a seller’s fee, was far higher than expected. The auction house had expected the portrait to go for no more than $400,000.

Melissa McCracken, a spokeswoman from the auction house, said: “There’s only one photo of Billy the Kid, and I think that’s why it captivates people’s imagination.”

The photograph is believed to have been given by Billy the Kid – who was also known as William Henry McCarty, Henry Antrim and William H Bonney – to his friend, Dan Dedrick, and had been the property of Dedrick’s descendants until the sale.

It shows the outlaw standing against a Winchester carbine rifle on one side with a Colt revolver holstered on his left, and wearing a black hat, waistcoat and bulky cardigan.

The image was only once publicly displayed at a museum in Lincoln County, New Mexico, where Billy the Kid began his infamous career as a gunman in the 1870s. He was later shot dead by Sheriff Pat Garrett in 1881 and is buried in Fort Sumner, New Mexico, where the photograph is believed to have been taken.

The tintype format was an early type of photography which used metal plates to create reverse images, and the photograph led to the mistaken belief that the outlaw was left handed. This is why a 1958 film about his life, starring Paul Newman, was entitled The Left Handed Gun.

The picture was one lot in an auction of more than 400 western-themed items, including documents about Buffalo Bill’s near divorce and Andy Warhol’s Cowboys and Indians series, depicting a Navajo woman with a baby on her back.